1. Field of the Invention
The present disclosure is generally directed to an improvement to sealing gravel exit ports in gravel pack assemblies, and more specifically, to a system and method for providing a seal for exits ports in gravel pack assemblies.
2. Description of the Related Art
It is common practice in the art of subterranean oil well completion to deposit gravel in an annular space between a gravel pack screen and an inner surface of a wellbore casing at a production zone to form a gravel pack, if the surrounding formation has pervasive sand and/or other particulates. Due to its abrasive nature, formation sand in the production fluid is detrimental to downhole completion equipment and surface production equipment. The gravel pack may be used to filter out the particulates. Gravel packing comprises packing with gravel the annulus between the perforated casing or openhole wellbore and slotted screens, a gravel pack screen, positioned opposite the perforations or desired formation, proximate to a production tubing opening, to form a filter for reducing the flow of formation sand into the wellbore.
In conventional methods of gravel packing, a gravel pack slurry is displaced down the tubing string and through the gravel pack assembly to deposit the gravel in wellbore perforations or openhole annulus and in an annular space between the casing or wellbore and the gravel pack screen attached to the gravel pack assembly. The gravel slurry exits the gravel pack assembly into the annulus through at least one gravel exit port. Typically, such gravel exit ports comprise a hole through a portion of the gravel pack assembly housing. The hole of a gravel pack exit port is typically larger than the size of the aggregate gravel to allow free flow there through while the gravel packing procedure is carried out. After depositing the gravel pack, the gravel ports are closed and sealed with a gravel exit port seal so that other wellbore completion operations may be carried out. Typically, a gravel exit port seal comprises a sleeve with at least two sealing elements, such as o-rings. The exit port seal sleeve is typically located in an internal bore of the gravel pack assembly housing on an internal surface of the housing and may vertically slide within the bore. While gravel slurry is passing through the gravel port and being deposited in the wellbore, the gravel pack seal sleeve remains adjacent to the gravel port in an “open” position permitting flow through the gravel port. The exit port seal closes by the sleeve sliding over the exit port, thus covering it, positioning sealing elements above and below the exit port. Other port systems may use a rotating sleeve or have an external sliding mechanism or some other external sealing means.
The prior art gravel exit port seal described above may potentially fail due to repeated use, the abrasive nature of the gravel slurry, or other conditions in the wellbore. Further, there exits the potential that the sleeve may not function properly failing to move to the “closed” position at the completion of the gravel packing procedure or inadvertently being moved to the open position during other wellbore completion operations permitting communication between the bore of the gravel pack assembly and the annulus containing the gravel pack. Thus, it is a common practice to employ a secondary gravel exit port seal mechanism. Such secondary seals are known in the prior art as “straddle seals” because they form a seal against the inner surface of the gravel pack assembly housing above and below the gravel exit ports. The straddle seal comprises a housing having a plurality of sealing elements, such as o-rings or molded seals, around its outer circumference. The straddle seal is positioned within the gravel pack assembly bore such that the plurality of sealing elements mate and seal with a seal bore on the inner surface of the gravel pack housing assembly located above the gravel exit port and a seal bore on the inner surface of the gravel pack housing assembly located below the gravel exit port. The sealing elements prevent the flow of gravel out of the annulus into the production bore in the event that the gravel exit port seal fails or is not properly located in the closed position.
The secondary seal housing further includes an inner bore permitting the production of hydrocarbons from the well formation. Because the straddle seal occupies space inside the gravel pack assembly bore, the effective internal cross-sectional area of the gravel pack assembly is reduced, which may detrimentally affect hydrocarbon production efficiency or other wellbore completion operations. The secondary seal assembly is set after the gravel pack has been deposited within the well bore. To set the secondary seal, a setting tool must be run down the work string. This additional trip down the work string requires additional rig costs and may take up a large amount of time, thereby prohibiting production during this time and increasing the operating costs of the well completion.
Thus, what is needed is a secondary or novel primary sealing mechanism that reliably seals the gravel pack assembly gravel exit port without constricting the inner cross-sectional area of the gravel pack assembly and without requiring an additional trip down the well to set.
The present disclosure is directed to an apparatus and method for solving, or at least reducing the effects of, some or all of the aforementioned problems.